The 20-year-old from Kettering started the final round with a one-shot lead over American Brittany Lincicome and South Korea's Ryu So-yeon, and produced a brilliant, bogey-free 66 to finish on 19 under par at Tiburon Golf Club.
Hull had six birdies on the outward nine and three on the back nine en route to a new tournament scoring record, previously set in 2015 by Cristie Kerr at 17 under.
Hull and Ryu were locked together on 18 under with two holes to play, but a two-shot swing at the par-five 17th - Hull rolled her approach up for birdie while Ryu found a greenside bunker and could only manage a bogey - turned proceedings decisively in the Briton's favour.
Ryu admitted to making a mistake with her shot selection.
"The good thing is when you decide to do something and you completely have faith in it then when you do it you cannot really complain about the result," she said.
"Maybe the 17th was my only decision that wasn't really great... But sometimes I feel like God just made that happen. God can make that happen to make be a better player, make me a better person.
"So I just really don't want to blame myself. I just take this one as just serendipity, you know."
Hull was bogey-free throughout the tournament, carding 12 birdies.
This is her second title since turning professional, following the Lalla Meryem Cup on the Ladies European Tour in 2014.Reuse content